This invention relates to novel 2,7-dihalofluorenes which are substituted at the 9-position and methods for the preparation of such 9-substituted-2,7-dihalofluorenes. This invention further relates to oligomers and polymers of such fluorene compounds. This invention also relates to films and coatings prepared from such fluorenes, oligomers and polymers, processes for preparing such films and coatings, and light-emitting diodes comprised of one or more layers of polymer films at least one of which is derived from the oligomers and polymers of the invention.
Polymers and oligomers of fluorenes substituted by alkyl groups at the 9-carbon position have been reported by Fukuda et al. in Japanese Journal of Applied Physics, Vol. 28, pp. L1433-L1435 (1989). Such polymers are disclosed as useful as luminescent materials in the preparation of light-emitting diodes. These polymers were prepared by the Kovacic procedure wherein the appropriate fluorene monomers were treated for several days with a large excess of oxidizing metal salts such as ferric chloride. The structures are represented as poly(fluorene-2,7′-diyl)s. In a later article, Fukuda disclosed that the procedure used resulted in significant crosslinking and mislinking reactions during the polymerization. See Fukuda et al., Journal of Polymer Science, Polymer Chemistry Edition, Vol. 31, pp. 2465-2471 (1993). Brown et al., Journal of Polymer Science Polymer Chemistry Edition, Vol. 24, pp. 255-267 (1989) disclosed the presence of substantial chemical defects in the polymers formed by oxidative coupling polymerization of aromatic compounds under the reaction conditions of the Kovacic procedure, resulting in non-regioselective coupling and a significant number of polynuclear structures. Thus, it may be expected that oxidative coupling of fluorenes may frequently occur through other, non-desirable, positions, such as the 3,5′- and 3,6′-positions. In addition, it is possible that branching may occur as a result of attachment of more than two other fluorene molecules to a given fluorene molecule, thereby creating multifunctional sites for growth of branches. The presence of such by-products can result in low molecular weight oligomers and polymers with low degrees of polymerization. Such materials demonstrate a high polydispersity and low glass transition temperatures, properties that are detrimental to film quality. Indeed, Fukuda's polyfluorenes prepared by oxidative coupling have high polydispersity and low glass transition temperatures. Furthermore, the oxidative coupling process is very slow.